Articles such as preformed concrete building blocks, roof and floor tiles, paving slabs, structural members, and other articles have traditionally been formed from concrete comprising a mixture of cement, such as hydraulic or Portland cement, mineral aggregate, and water, plus various optional additives such as air entraining agents, water reducers, plasticizers, water proofing and possibly others. These materials may in some instances be combined with reinforcement such as steel bars, wires or fibres. The materials are generally blended in a concrete mixer and the resultant wet mixture is placed and densified in a mould or form to produce a desired shape. Hydration of the cement paste then takes place over a period of time after which the mould or form is removed to form the concrete article. Concrete formed in this manner has reasonable strength and durability in most environments.
Sulphur is readily available in many countries as a by-product of the oil and gas industry. The relatively low cost and unique properties of sulphur have led to its utilization as a construction material particularly to replace the use of Portland cement or asphalt cement. Sulphur concretes have been developed in which elemental or modified sulphur completely replaces the Portland cement as binder.
The sulphur used in such products is typically modified or plasticised in order to prevent allotropic transformation of the solid sulphur. Modified sulphur is typically prepared by reacting a portion of the sulphur with a sulphur modifier, also referred to as sulphur plasticiser. A well-known category of sulphur modifiers are olefinic compounds that co-polymerise with sulphur. Known examples of such olefinic modifiers are dicyclopentadiene, limonene, styrene or naphthalene. Reference is for example made to B. R. Currell et al. “Plasticization of Sulfur” In: J. R. West (ed.), Preceedings of symposium “New Uses of sulphur”, Los Angeles, April 1974, Advances in Chemistry Series No. 140, Am. Chem. Soc., Washington, 1975, p. 1-17. Other examples of olefinic modifiers are 5-ethylidene-2-norbornene and 5-vinyl-2-norbornene as described in WO2006/134130.
Plasticised or modified sulphur may be used in the form of a so-called concentrate, i.e. sulphur reacted with a relatively high amount of modifier. For the preparation of the sulphur-bound product, e.g. concrete, the concentrate is then mixed at a temperature above the melting temperature of sulphur with further sulphur, filler and aggregate, and solidified.
Unfortunately, sulphur-bound products such as modified sulphur and sulphur concrete tend to suffer from the disadvantage of having an undesirable odour. This is due to the emission of sulphur-containing gases such as H2S, SO2 and mercaptans (such as methyl mercaptan and ethyl mercaptan) from both modified sulphur and sulphur concrete during and after manufacture. This odour is particularly undesirable in the case of sulphur concrete if it is to be used in any setting where people come into contact with it, e.g. paving slabs, tiles, walls etc. Therefore there is a need for providing modified sulphur and sulphur concrete having a reduced odour.
It has now surprisingly been found by the present inventors that if sulphur-bound products, such as modified sulphur or sulphur concrete, are contacted with a suitable bleaching agent the odour of these products is reduced.